Proponents of a proposed ballot measure aimed at making California the fifth state to legalize pot for recreational use are a few weeks away from kicking off their November 2016 campaign, supporters said Thursday.

Once the marijuana legalization coalition known as ReformCA files its initiative with the state Attorney General’s Office, the group can begin gathering the 365,000 valid signatures it will need to put a proposition on the ballot — something coalition chairwoman Dale Sky Jones says she’s confident it can do.

Four other initiatives with the same goal have already been cleared for circulation, but this is the one that’s expected to attract top donors and major interest from a huge network of grass-roots supporters.

“We have been working on the plan to make a strong run at the ballot box,” said Sky Jones, the executive director of Oaksterdam University, the country’s first college devoted to instruction about cannabis.

During a conference call with reporters, Sky Jones said she thinks it will take up to $14 million to run a successful campaign, but she released few details about who the top donors might be or what the initiative will look like — other than to say that it seeks to control, tax and regulate recreational marijuana. The initiative would also write rules for California’s decades-old medical marijuana industry, she said.

“California is long overdue,” she said, adding that Colorado and Washington state have had few problems since voters passed similar laws in 2012. Voters in Alaska, Oregon and the District of Columbia legalized recreational pot use in November.

California voters rejected marijuana legalization in November 2010, but a recent Public Policy Institute of California poll showed that attitudes on the issue have shifted, with 55 percent of likely voters now supporting legalization.

But as public support for the weed grows, so does the concern about underage use. The National Institute on Drug Abuse’s 2014 annual survey found 34 percent of 10th-graders and 44 percent of 12th-graders had used marijuana.

But that’s a compelling case for legalization and regulation, argues Lt. Gov. Gavin Newsom, a Democratic candidate for governor in 2018 and chairman of the American Civil Liberties Union’s task force on marijuana legalization. The group is expected to release a report with recommendations as soon as next month.

The campaign’s success will hinge in part on tapping into Californians’ passion for pot legalization, and that’s why ReformCA hired Joe Trippi, a veteran political consultant who became a household name a decade ago when he ran former Vermont Gov. Howard Dean’s presidential campaign.

On Thursday’s conference call with reporters, Trippi said the group has already amassed an e-mail list of 70,000 supporters without spending a dime on advertising.

“Too often, people wait too long to build their digital army,” said Trippi, referring to the list of supporters he plans to solicit for small donations. “Our legalization effort will be a well-thought-out, disciplined campaign.”